Read File line by line to variable and loop

Question

I have a phone.txt like:

09236235965
09236238566
09238434444
09202645965
09236284567
09236235965
..and so on..

How can I process this data

Answer 1

Read the comments inline please. They will explain what is going on to assist you in learning how this works (hopefully):

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>

int main(int argc, char *argv[])
{
    // open the file if present, in read mode.
    std::ifstream fs("phone.txt");
    if (fs.is_open())
    {
        // variable used to extract strings one by one.
        std::string phonenum;

        // extract a string from the input, skipping whitespace
        //  including newlines, tabs, form-feeds, etc. when this
        //  no longer works (eof or bad file, take your pick) the
        //  expression will return false
        while (fs >> phonenum)
        {
            // use your phonenum string here.
            std::cout << phonenum << '\n';
        }

        // close the file.
        fs.close();
    }

    return EXIT_SUCCESS;
}

Answer 2

Simple. First, note that you want an ifstream, not an ofstream. When you're reading from a file, you're using it as input - hence the i in ifstream. You then want to loop, using std::getline to fetch a line from the file and process it:

std::ifstream file("phone.txt");
std::string phonenum;
while (std::getline(file, phonenum)) {
  // Process phonenum here
  std::cout << phonenum << std::endl; // Print the phone number out, for example
}

The reason why std::getline is the while loop condition is because it checks the status of the stream. If std::getline fails in anyway (at the end of your file, for example), the loop will end.

Answer 3

You can do that :

 #include <fstream>
 using namespace std;

 ifstream input("phone.txt");

for( string line; getline( input, line ); )
{
  //code
}